Backlight unit for dynamic image and display employing the same

ABSTRACT

A backlight unit for a dynamic image and a display employing the same are provided. The backlight unit is used for a light source of a display and includes light-emitting devices located separately on a substrate, an image analyzer which analyzes an image signal and extracts position information on a region requiring the relative increase or decrease of brightness, and a control unit which independently drives and controls the light-emitting devices located in a region corresponding to the position information inputted from the image board. Accordingly, the display employing the backlight unit can provide a more dynamic and realistic image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Korean Patent Application No.10-2005-0034566, filed on Apr. 26, 2005 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight unit and a displayemploying a backlight unit, and more particularly, to a backlight unitthat provides a dynamic image by properly controlling the brightness oflight emitting devices that can be driven independently with respect toan image having a large difference of brightness, and a displayemploying the backlight unit.

2. Description of the Related Art

Liquid crystal displays (LCDs) are used in notebook computers, desktopcomputers, LCD-TVs, mobile communication terminals, and so on. Since anLCD is a light receiving element type display that cannot emit light byitself, the LCD needs a backlight unit in addition to a liquid crystalpanel. The backlight unit is located in the rear of the liquid crystalpanel and emits light onto the liquid crystal panel.

The backlight unit can be classified as a direct light type backlightunit and an edge light type backlight unit in accordance with thearrangement of a light source. The direct light type backlight unitirradiates light from a plurality of light sources provided under theliquid crystal panel toward the liquid crystal panel. The edge lighttype backlight unit emits light from a light source located at asidewall of a light guide panel (LGP) to the liquid crystal panel. Acold cathode fluorescent lamp (CCFL) is generally used as the lightsource for the edge light type backlight unit.

Meanwhile, a light emitting diode (LED) is considered as a substitutefor the CCFL. For example, LEDs emitting Lambertian light are used as apoint light source for the direct light type backlight unit.

Referring to FIG. 1, a conventional backlight unit includes an LED 500,a diffusion plate 503 and a diffusion sheet 505 for projecting lightemitted from the LED 500 onto a liquid crystal panel 510 to be uniform,and a reflection plate 502 for reflecting light that is emitted from theLED 500 to proceed toward the liquid crystal panel 510 located above LED500. Further, a prism sheet 507 is provided to correct a lighttravelling route between the diffusion sheet 505 and the liquid crystalpanel 510 and cause the emitted light to proceed toward the liquidcrystal panel 510.

In an LCD, however, a slow response time of the liquid crystal resultsin a motion blur phenomenon in a fast moving picture. Since the amountof light from a conventional backlight unit is identical over the entiresurface of the LCD, an image is monotonous as a whole. For example, foran image that requires a partial increase of the brightness, as in anexplosion scene, or an image that requires a partial decrease of thebrightness, as in a starlit night sky as a background, there is alimitation in representing the images vividly.

Specifically, eight CCFLs arranged in a line are required for a 26-inchdisplay, and sixteen CCFLs for a 32-inch display. In order to controlthe brightness, the CCFLs as a line light source need to control eachcurrent applied thereto. However, all CCFLs are connected in series andit is impossible to finely control a region needing the increase ordecrease of the brightness, even though the CCFLs are drivenindependently. Consequently, the CCFLs cannot provide a dynamic image.

Also, in the case of a backlight unit using LEDs as a light source, allLEDs are connected and driven in series. Accordingly, it is possible todecrease or increase the overall brightness of LEDs, but it isimpossible to increase and decrease the brightness properly.

As described above, because the conventional backlight unit cannotprovide an image needing a partial increase or decrease of brightness,it is difficult to provide a dynamic image.

SUMMARY OF THE INVENTION

The present invention provides a backlight unit capable of providing adynamic image by controlling the brightness of light-emitting devicesseparately according to image signals.

According to an aspect of the present invention, there is provided abacklight unit for a light source of a display, the backlight unitincluding: a plurality of light-emitting devices which are disposed on asubstrate and driven separately; an image analyzer which analyzes animage signal and extracts position information corresponding to a regionof an image requiring a relative increase or decrease of brightness; anda control unit which independently drives and controls light-emittingdevices, among the plurality of light-emitting devices, which arelocated in the region corresponding to the position information which isextracted by the image analyzer.

The control unit may control the brightness of the plurality oflight-emitting devices by adjusting a voltage and/or a current appliedto the light-emitting devices.

The control unit may control the brightness of the plurality of lightemitting devices by supplying a higher or lower voltage or current tothe light-emitting devices, among the plurality of light-emittingdevices, which are located in the region corresponding to the positioninformation which is extracted by the image analyzer relative to voltageor current which is supplied to light-emitting devices which are notlocated in the region corresponding to the position information.

The light-emitting devices may include light-emitting diode (LED) chipsemitting light having at least two wavelength ranges, and the LED chipsare packaged on a base.

The LED chips may be disposed at a periphery of the base.

According to another aspect of the present invention, there is provideda display including: a plurality of light-emitting devices disposed on asubstrate and driven separately; an image analyzer which analyzes animage signal and extracts position information which corresponds to aregion of an image which requires a relative increase or decrease ofbrightness; a control unit which independently drives and controlslight-emitting devices, among the plurality of light-emitting devices,which are located in the region which corresponds to the positioninformation which is extracted by the image analyzer; and a displaypanel which displays an image using light emitted from the plurality oflight-emitting devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will become moreapparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 is a sectional view of a conventional direct light type backlightunit;

FIG. 2 is a sectional view of a display according to an exemplaryembodiment of the present invention;

FIG. 3 is a view illustrating the arrangement of multi-chip lightemitting devices used in a display and a backlight unit according to anexemplary embodiment of the present invention;

FIG. 4A is a perspective view of the light-emitting device used in thedisplay and the backlight unit according to an exemplary embodiment ofthe present invention;

FIG. 4B is a sectional view of the light-emitting device shown in FIG.4A;

FIG. 5 is a view illustrating the arrangement of single-chiplight-emitting devices used in a display and a backlight unit accordingto an exemplary embodiment of the present invention;

FIG. 6 is a flowchart illustrating the process of forming an image inthe display according to an exemplary embodiment of the presentinvention; and

FIG. 7 is a block diagram of the display according to an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS OF THE INVENTION

Exemplary embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIG. 2 is a sectional view of a display according to an exemplaryembodiment of the present invention.

Referring to FIG. 2, a display 100 includes a display panel 70 fordisplaying an image and a backlight unit 1 for providing light to thedisplay panel 70.

A liquid crystal display (LCD) can be used as the display panel 70. TheLCD includes thin film transistors and electrodes in each pixel anddisplays an image. An electric field is applied to liquid crystals inunits of pixels according to an image signal inputted from an imagesignal processor (not shown), and light emitted from the backlight unit1 is space-modulated. Through these procedures, an image is displayed.

The backlight unit 1 includes a plurality of light-emitting devices 15arranged two-dimensionally on a PCB substrate 20 and a control unit 18controlling the light-emitting devices 15. The light-emitting devices 15are driven electrically and separately and the control unit 18 controlsthe driving of the light-emitting devices 15. Also, a diffusion plate 40and a prism sheet 50 are located between the light-emitting devices 15and the display panel 70. The diffusion plate 40 uniformly projects thelight emitted from the light-emitting devices 15 onto the display panel70. The prism sheet 50 corrects a light travelling path and guides thelight toward the liquid crystal panel 70. A polarization enhancementfilm 60 may be further provided between the prism sheet 50 and thedisplay panel 70. The polarization enhancement film 60 enhances apolarization property to improve an optical efficiency.

As shown in FIG. 3, the light-emitting devices 15 are arrangedtwo-dimensionally on the PCB substrate 20. A larger number oflight-emitting devices 15 provide a higher resolution. Thelight-emitting devices 15 are formed on the PCB substrate 20 such thatcurrent is separately supplied to the PCB substrate 20. In addition, thecontrol unit 18 controls current or a voltage for the light-emittingdevices 15. For example, the brightness of the light-emitting devicesincluded in a region A of FIG. 3 can be increased or decreased more thanthat of the other light-emitting devices by supplying relatively higheror lower current or voltage to the light-emitting devices of the regionA than to the other light-emitting devices.

Referring to FIGS. 4A and 4B, the light-emitting devices 15 may be amulti chip light-emitting device where a plurality of LED chips 5emitting light with at least two wavelength ranges are configured in onepackage. Also, the light-emitting device 15 includes a cap 10 for totalreflection of the light emitted from the LED chips 5. The light-emittingdevices 15 generate a white light by totally reflecting the light withdifferent wavelengths several times in the LED chips 5 and mixing thelight.

In the light-emitting device 15, the LED chips 5 are arranged on a base7, and the cap 10 is located above the LED chips 5. The LED chips 5 emitlight with at least two different wavelength ranges. For example, theLED chips 5 may include a first LED chip 5 a emitting light with a redwavelength range, a second LED chip 5 b emitting light with a greenwavelength range, and a third LED chip 5 c emitting light with a bluewavelength range. In FIG. 4A, the light-emitting device 15 includeseight LED chips: three first LED chips 5 a, two second LED chips 5 b,and three third LED chips 5 c. The number or arrangement of LED chips 5in each wavelength range can be properly determined according to desiredcolor temperature ranges in consideration of an amount of light emittedfrom LED chips 5 in each wavelength. Thus, although the light-emittingdevices 15 are configured in a multi-chip structure, the size of themulti-chip structure does not vary remarkably in comparison with asingle-chip structure, so that the size of the light-emitting devices 15does not increase. In addition, since colors are mixed into a whitelight in the light-emitting device, a space for mixture becomes smaller.Consequently, a thickness of the backlight unit can be reduced.

The cap 10 is formed of transparent materials, for example, a lens. Thecap 10 is formed of materials having a larger refractive index than amedium between the light-emitting device 15 and the diffusion plate 40so as to satisfy the condition for a total reflection. For example, whenair is a medium between the light-emitting device 15 and the diffusionplate 40, the cap 10 can be formed of epoxy resin or poly-methylmethacrylate (PMMA), which has a refractive index of 1.49. Since the cap10 has a larger refractive index than air, the cap 10 totally reflectsseveral times the light that is projected at a larger angle than acritical angle on its boundary. Light from the light-emitting devices 15is mixed in the cap 10 and emitted as a white light. Thus, because thedifferent wavelengths of light are mixed in the cap 10 and emitted fromthe light-emitting diode units toward the diffusion plate 40, there isno need to mix light between the light-emitting devices 15 and thediffusion plate 40. Therefore, a distance between the light-emittingdevices 15 and the diffusion plate 40 can be shortened.

The cap 10 may be formed in a cone shape, a dome shape or a poly-pyramidshape. In FIGS. 4A and 4B, the cap 10 is formed in a cone shape.

Since the LED chips 5 a, 5 b and 5 c may be disposed not at the centerbut at the periphery of the base 7, the generation of a bright lightspot can be prevented. The bright light spot is a phenomenon in which arelatively bright spot is produced because the light from thelight-emitting device 15 is irregularly diffused and then is projectedwith a relatively high brightness. This bright light spot is one offactors which results in a low picture quality. When light is emittedfrom the LED chip 5 located at the center of the base 7, most of thelight is projected toward an apex of the cap 10 and transmitted withouttotal reflection. That is, if the LED chip 5 is located at the center ofthe base 7 opposite to the center of the cap 10, most of the lightemitted from the light-emitting device is incident at a smaller anglethan the critical angle of the cap 10. Thus, the light goes straightthrough the cap 10 or is refracted. On the other hand, if the LED chip 5is located at the periphery of the base 7, most of the light emittedfrom the LED chip 5 is incident at a larger angle than the criticalangle of the cap 10 and is totally reflected inside.

Meanwhile, the light-emitting device 15 can be formed within a singlechip and the light-emitting devices emitting light with differentwavelengths can be arranged in turn. As shown in FIG. 5, a firstlight-emitting device 35 a emitting light with a first wavelength, asecond light-emitting device 35 b emitting light with a secondwavelength, and a third light-emitting device 35 c emitting light with athird wavelength are alternately arranged on a PCB substrate 30.Meanwhile, in some cases, when it is necessary to provide light withwavelength needing a greater light intensity than that of other light,two chips emitting light needing the greater light intensity can bearranged consecutively. For example, an amount of a green light can besupplemented by arranging a red light-emitting device, a greenlight-emitting device, a green light-emitting device, and a bluelight-emitting device in sequence.

As described above, the single-chip light-emitting devices 35 a, 35 band 35 c are driven electrically and separately through a control unit37 on the PCB substrate 30.

For example, the brightness of the light-emitting devices included in aregion B of FIG. 5 can be increased or decreased more than that of theother light-emitting devices by supplying a relatively higher or lowercurrent or voltage to the light-emitting devices of the region B than tothe other light-emitting devices. Accordingly, a more dynamic image canbe provided.

FIG. 6 is a flowchart illustrating a process of forming an image in thedisplay according to an exemplary embodiment of the present invention.Further, FIG. 7 is a block diagram of the display according to anexemplary embodiment of the present invention. In Operation 610, animage signal unit 710 inputs an image signal to an image board 720. InOperations 630 and 650, the image board 720 analyzes the image signaland determines whether the image requires an increase or decrease to thebrightness. A reference value that is used for determining the increaseand decrease of the brightness is stored in the image board 720, andinformation of a region that requires an increase or decrease to thebrightness is extracted from the reference value. In Operation 670, inthe case of an explosion scene or firework scene, for example, thebrightness must be partially increased more than in the other regions ofthe display. Conversely, in the case of a starlit night sky, thebrightness as a background must be decreased relative to other regions.In these cases, position information of the corresponding regions istransferred to a control unit 730. In Operation 680, the control unit730 adjusts the brightness of the light-emitting devices by controllinga driving current and/or voltage of each of light-emitting devices 740in the region that corresponds to the position information. Next, adisplay panel 750 performs a space modulation on the light emitted fromthe light-emitting devices 740 according to the image signal that isinput from the image signal unit 710 and then outputs the resultingimage. As described above, according to an exemplary embodiment of thepresent invention, a realistic image is provided by controlling abrightness of light-emitting devices that correspond to the region thatrequires an increase or decrease of brightness.

According to an exemplary embodiment of the present invention, thelight-emitting devices can be independently driven and controlled.Therefore, the images that are subject to partial increase or decreaseof the brightness can be displayed more dynamically and realistically bycontrolling the current applied to the light-emitting devices.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A backlight unit for a light source of a display, the backlight unitcomprising: a plurality of light-emitting devices which are disposed ona substrate and driven separately; an image analyzer which analyzes animage signal and extracts position information corresponding to a regionof an image requiring a relative increase or decrease of brightness; anda control unit which independently drives and controls light-emittingdevices which are located in the region corresponding to the positioninformation which is extracted by the image analyzer to increase ordecrease the brightness more than that of light-emitting devices whichare not located in the region corresponding to the position information;wherein each of the plurality of light-emitting devices compriseslight-emitting diode (LED) chips which emit light having at least twowavelength ranges and a cone-shaped cap which covers the LED chips,wherein the LED chips are packaged on a base of the light-emittingdevice and are disposed at a periphery of the base, wherein the cap hasa larger refractive index than a refractive index of an adjacentexternal medium, and the cap totally reflects at least some of the lightemitted from each LED chip several times.
 2. The backlight unit of claim1, wherein the control unit controls the brightness of the plurality oflight-emitting devices by adjusting a voltage or a current which isapplied to the plurality of light-emitting devices.
 3. The backlightunit of claim 2, wherein the control unit controls the brightness of theplurality of light emitting devices by supplying a higher or lowervoltage or current to the light-emitting devices which are located inthe region corresponding to the position information which is extractedby the image analyzer relative to voltage or current which is suppliedto the light-emitting devices which are not located in the regioncorresponding to the position information.
 4. The backlight unit ofclaim 1, further comprising a diffusion plate which projects lightemitted from the light-emitting devices as uniformly incident on adisplay panel.
 5. The backlight unit of claim 1, wherein the light thatis totally reflected several times is subsequently emitted from a sideof the cap.
 6. A display comprising: a plurality of light-emittingdevices which are disposed on a substrate and driven separately; animage analyzer which analyzes an image signal and extracts positioninformation corresponding to a region of an image requiring a relativeincrease or decrease of brightness; a control unit which independentlydrives and controls light-emitting devices which are located in theregion corresponding to the position information which is extracted bythe image analyzer to increase or decrease the brightness more than thatof light-emitting devices which are not located in the regioncorresponding to the position information; and a display panel whichdisplays an image using the light emitted from the plurality oflight-emitting devices; wherein each of the plurality of light-emittingdevices comprises light-emitting diode (LED) chips which emit lighthaving at least two wavelength ranges and a cone-shaped cap which coversthe LED chips, wherein the LED chips are packaged on a base of thelight-emitting device and are disposed at a periphery of the base, andwherein the cap has a larger refractive index than a refractive index ofan adjacent external medium, and the cap totally reflects at least someof the light emitted from each LED chip several times.
 7. The display ofclaim 6, wherein the control unit controls the brightness of theplurality of light-emitting devices by adjusting a voltage or a currentwhich is applied to the plurality of light-emitting devices.
 8. Thedisplay of claim 6, wherein the display panel is a liquid crystaldisplay.
 9. The display of claim 7, wherein the control unit controlsthe brightness of the plurality of light emitting devices by supplying ahigher or lower voltage or current to the light-emitting devices whichare located in the region corresponding to the position informationwhich is extracted by the image analyzer relative to voltage or currentwhich is supplied to light-emitting devices which are not located in theregion corresponding to the position information.
 10. The display ofclaim 6, wherein the light that is totally reflected several times issubsequently emitted from a side of the cap.